1. Field of the Invention
The present invention relates to a wide-band amplifier circuit with improved gain flatness, which is applicable to a 3rd Generation Partnership Project Long-Term Evolution (3GPP LTE) system, and more particularly, to a wide-band amplifier circuit with improved gain flatness, which satisfies a requirement for a wide band in a band less than 1 GHz in an upload link frequency band while having high gain flatness.
2. Description of the Related Art
3GPP LTE communications systems, considered to be 4G technology, are techniques that aim at supporting various services based on packet data transfer. The 3GPP LTE communications systems support a downlink peak data rate of 100 Mbps and an upload link data rate of 50 Mbps with reference to a maximum bandwidth of 20 MHz. 3GPP LTE communications systems ensure improved data rates, low latency, efficient use of frequency resources, mobility, techniques optimized for packet data transfer, and high service quality.
Such 3GPP LTE systems are mobile communications systems suitably evolving for IP networks, so that frequencies and high-speed multimedia services can be used more efficiently than by existing systems. 3GPP LTE mobile communications terminals support a downlink data rate of 30 Mbps and an upload link data rate of 15 Mbps at a mobile speed of 120 km/h in 20 MHz bandwidth. The 3GGP LTE communications terminals provide high-quality high-speed multimedia services and are thus capable of providing mobile image services unlike 3.5G high-speed downlink packet access (HSDPA).
As for bands of less than 1 GHz in the upload link frequency band of a 3GPP LTE communications system, there are total six bands: Band 5 (824 MHz to 849 MHz), Band 6 (830 MHz to 840 MHz), Band 8 (880 MHz to 915 MHz), Band 12 (698 MHz to 716 MHz), Band 13 (777 MHz to 787 MHz) and Band 14 (788 MHz to 798 MHz). A bandwidth from 697 MHz to 915 MHz, including band spacing, that is, a bandwidth of 217 MHZ, is required.
One example of the related art is a low noise amplifier (LNA) used for an ultra wide band (UWB) using a band between 3 GHz and 10 GHz. The LNA amplifies a signal by using an inverter structure, and obtains a wide-band characteristic by using one of two feedback paths. A capacitive parallel feedback path realizes a low and medium frequency range, and an inductive series feedback path realizes a high frequency range, so that the amplifier satisfies the wide band of about 7 GHz.
This related art LNA, having the above feedback structure, achieves high linearity, but has limitations in that it is difficult to implement high gain, and additional circuits and currents need to be added for feedback.
Another example of the related art is an LNA used for 802.11a systems. This LAN has a frequency band from 5.1 GHz to 5.9 GHz, and employs a 2-stage amplifier having a cascode structure. The gain flatness desirably reaches 0.06 dB in this band.
However, a relatively large number of inductors are used in order to obtain a flat gain. This expands the chip size, thereby increasing the unit cost of a chip.